Oscillatory circuit



Dec. 27, 1949 R. G. HIBBERD 2,492,748

OSCILLATORY CIRCUIT Filed Nov. 14, 1945 inventor:

b MW 47% His Attorney.

Robert G. Hibberd, I

Patented Dec. 27, 1949 OSCILLATORY CIRCUIT Robert G. Hibberd, Rugby,England, assignor to General Electric Company a corporation of New YorkApplication November 14, 1945, Serial No. 628,565 In Great BritainDecember 19, 1944 Claims. 1 This invention relates to thermionic valveos-' cillation generators adapted for the generation of oscillations ofultra high frequency.

In such oscillation generators, it is important to avoid the generationof oscillations of spurious frequencies and to eliminate unwantedcapacity and inductance in the circuit. This generally involves the useof push-pull circuits which are very carefully balanced.

One satisfactory circuit which has become known in the art is what hasbeen termed a "butterfly oscillator. Such an oscillator isdiagrammatically illustrated in Fig. 1 of the accompanying drawing. Itcomprises a split-stator variable condenser having a rotor l and stator2 in combination with inductances 3 symmetrically connected between thetwo sections of the stator 2 of the condenser. The rotor of thecondenser is connected to earth at 4. A pair of thermionic valves havetheir anodes 5 connected to the respective sections of the stator, theircathodes 6 connected through radio frequency choke coils 1 to earth at8, and their grids also connected to earth through a resistance 9. Thecathode heaters are also connected through radio frequency choke coils 1and Ill to a source of heating current at H. Anode potential is suppliedfrom the source of positive potential B+ through a radio frequency chokecoil I2 to the middle of one of the inductances 3 as indicated. It willbe observed that this circuit is perfectly balanced electrically, but inorder to obtain the optimum results therefrom it is also necessary toarrange symmetrically the components therein to obtain physical as wellas electrical balance. Furthermore, for the generation of ultra highfrequency oscillations the inductance in the oscillatory circuit must bereduced to a very low value.

In butterfly oscillator circuits as hitherto used, for wave-lengths ofthe order of a decimeter, a condenser having plates of the formillustrated in Fig. 2 has been employed. In this construction the rotorplates l interleave with stator plates 2 which are interconnected attheir periphery by portions 2a which constitute the inductances 3 of thecircuit illustrated in Fig. 1. Thus for any given circuit, the ratio ofinductance to capacity is fixed. Furthermore, a condenser of thecharacter shown in Fig. 2 is difficult to In an oscillatory circuit fora "butterfiy oscillator comprising a split stator condenser and a pairof inductances according to the invention the inductances areconstituted by a pair of metal plates symmetrically arranged withrelation to the condenser, each plate being connected at its oppositeedges to regions of opposite potential on the fixed'plates of thecondenser, the contour of the plates following that of the outer edgesof the fixed and movable plates. The inductance plates may besubstantially coextensive with the stator of the condenser and by thusextending the superficial area of the plates the inductance thereof isreduced to a value commensurate with the capacity of the condenser,

thereby enabling the generation of ultra high Y frequencies. 7

In order to maintain balance in the circuit of the oscillator, the pairof valves is located symmetrically with respect to, and with theirlongitudinal axes substantially parallel with, the axis of rotation ofthe condenser rotor, the anodes being connected as directly as possibleto the respective sections of the split-stator.

In order to adjust the range of 1 frequency through which the'oscillatoris tunable, the inductance plates are preferably provided withadjustable supporting means so that the spacing between these plates andthe plates of the condenser can be varied.

This may conveniently be effected by flanging the edges of the platesand forming slots in the flanges. The slots engage on set screws whichattach the plates to the respective sections of the fixed plates of thecondenser and the slots permit of the adjustment of the plates towardsand away from the stator.

An important further feature consists in shortcircuiting the fixed andmoving plates at their edges in order to reduce the electrical length ofthe path along the plates which might constitute a resonant circuit at afrequency different from the operating frequency. This materiallyassists in the elimination of spurious frequencies.

To enable the invention to be readily understood I have illustrated inFig. 3 of the accom panying drawing in perspective view a practicalembodiment of the same; Fig. 4 indicates one form of plate for thesplit-stator condenser; and Fig. 5 is an explanatory diagram of themodification illustrated in Fig. 6; and Fig. '7 shows the application ofthe invention to a wave meter.

Indescribing Figs. 3 and 4, the same reference numerals are used as areemployed in describ ing Fig. 1 to indicate similar parts of the em--bodiment of the invention. The stator plates l3 of the condenser arespaced somewhat as indicated in Fig. i. Interleaving into the statorplates are the moving plates I mounted on the control shaft 14. Thestator plates i3 are, as shown in Fig. 3, clamped together with suitablespacing means by the longitudinal pillars l5 engaging headers l6. Theheaders 16 are of X- shape in end view. The header at the near end ofFig. 3 is formed by the channel-shaped insulating member l'l. Spacers [8separate the header I! from the nearest stator plates by a distancesuiiicient to permit of the mounting of the valves IS in the space soprovided. In the embodiment illustrated, these valves are of the acorntype and one is inverted with respect to the other. Spring contacts 20form the connections for the lead-through conductors which are broughtradially through the envelope in the customary manner. To these contactsare connected the radio frequency choke coils l and it] respectively.

The inductance plates 3 are shaped, as shown, to conform with thecontour of the fixed and moving plates of the condenser. It will benoted that the plates 3 are substantially coextensive with the fixedplates of the condenser. This extension of the superficial area of theplates materially reduces their inductance and brings it to a valuecommensurate with the capacity of condenser, thus enabling thegeneration of ultra high frequencies. They are flanged at 2|, theflanges being slotted to receive set screws 22 which secure the platesto the stator of the condenser and make the necessary electricconnections therewith. The slotting of the flanges permits theadjustment of the plates towards and away from the condenser plates,thereby enabling the range over which the oscillator is tunable to beadjusted.

In the arrangement above described, there exists the possibility ofspurious frequencies being generated by the circuit. It has been foundthat the circuit has two modes of resonance, the first or normal moderound the inductance plates being the fundamental mode normallyrequired, while the second mode is in space quadrature with thefundamental mode and is illustrated in the diagram shown in Fig. 5. Inthis figure, the adjacent plates of the stator are shown to formcondensers 24 in parallel with the inductance constituted by the plates3, thus providing a resonant circuit. It has been found that theunwanted. frequency resulting from the presence of this secondary modeis of the order of 3 times the fundamental and desired resonancefrequency.

A further important feature of the invention accordingly resides in theprovision of means for raising the frequency of these unwantedoscillations so that they are less harmful. To this end the edges of thefixed and moving plates of the condenser shown at 23 in Fig. 3 and areindicated more clearly in the view of Fig. 6. The unwanted frequenciesmay be damped out by loops 25 shown in Fig. 6 which couple these to butare in space quadrature with the fundamental mode.

In a circuit arrangement as above described using a split-statorcondenser of known construction with seven stator and six rotor platesand employing acorn" valves designated VRfiS, it was found that with theinductance plates 3 closed right in, the oscillator would tune from 280to 680 megacycles. With the plates 3 set at the maximum inductanceposition, it would tune are short-circuited by conductors from 230 t 620megacycles. The anode voltage employed was 160 volts, resistance 9 had avalue of 20,000 ohms, and chokes 1, I0, and I2, consisted each of 11turns of .020 enamelled wire on a 4 diameter former. Oscillations couldbe obtained with an anode voltage of as low as volts.

Fig. 7 shows the application of the butterfly oscillatory circuit to awavemeter. In this figure similar reference numerals have again beenused to indicate elements corresponding to those in the previousdiagrams. The oscillations to be measured are fed in through a loop 26which couples to one of the inductance plates 3. A crystal detector 7.1is connected in series with a condenser 28 (of about 2 mf. capacity forthe order of wave length above mentioned) across the oscillatory circuitand a micro-ammeter 29 is connected in series with the radio frequencychoke 3|} as indicated. The components may conveniently be mounted in ascreening metal box with the ammeter and tuning scales in juxtapositionso that they can be read easily by the operator. The box may be providedwith a socket (indicated at 3! in Fig. '7) into which an aerial of rodform may be plugged.

What I claim as new and desire to secure by letters Patent of the UnitedStates, is:

1. A balanced oscillatory circuit comprising a capacitor including anarcuate rotor plate and a pair of diametrically opposite stator platesextending beyond said rotor plates, a pair of symmetrically positionedinductor plates perpendicular to and overlying the edges of stator androtor plates, and means for adjustably connecting said inductor platesat opposite ends to the extending ends of said stator plates.

2. A balanced oscillatory circuit comprising a capacitor having a pairof stacks of stator plates arranged opposite each other, a plurality ofrotor plates between said stacks arranged for movement into interleavedrelation with the plates thereof, a pair of enclosing inductor platesperpendicular to said stator and rotor plates and having the generalcontour of the peripheral edges of said stator and rotor plates andembracing the ends of said stacks, and means connecting opposite ends ofsaid inductor plates to the outer ends of said stacks of stator plates.

3. A balanced oscillatory circuit comprising a capacitor including astack of spaced sectorshaped rotor plates and a pair of diametricallyopposite interleaving stacks of spaced stator plates extending beyondsaid rotor plates, and a pair of inductor plates substantially enclosingopposite peripheral edges of said rotor and stator plates and having thegeneral contour of said peripheral edges, said inductor plates beingelectrically connected at opposite ends to the ex ends of said statorplates.

4. A. balanced oscillatory circuit comprising a capacitor having a pairof diametrically opposite sector-shaped rotor plates and a pair ofdiametrically opposite sector-shaped stator plates having extendingbeyond said rotor plates, a pair of enclosing inductor plates havingopposite ends connected to the extending ends of said stator plates andhaving the general contour of the peripheral edges of stator and rotorplates, and means for adiustably positioning said inductor plates withrespect to the peripheral edges of said rotor and stator plates, therebyto tune said circuit to a desired frequency within a predetermined rangeof frequencies.

5 5. A balanced oscillatory circuit comprising 1;, REFERENCES CITEDcapacitor including a stack of spaced sectorshaped rotor plates and apair of diametrically The following references are of record in theopposite interleaving stacks of spaced stator me of pa'tent:

plates extending beyond said rotor plates, short- UNITED STATES PATENTScirculting means electncally connecting the edges of said stator androtor plates respectively, Number Name Date and a p ir of inductorplates substantially en- 6,8 8 Brown Aug. 16,, 1938 closing oppositeperipheral edges of said stator 2,135,672 Morris et 1938 and or platesand having the general contour m 7 aiOO May 30, 1939 of said peripheraledges, said inductor plates 2,235,010 Chime? 1941 being electricallyconnected at opposite ends to 2,341,345 Van Bllllal'd 1944 the extendingends of said stator plates. 2,367,631 Kal'plus e l- 4 ROBERT G. HIBBERD.9, 77 Raskhodoff Feb. 13, 1945

